According to the eccentric mechanism in the related art, (a) an eccentric disk is attached to an output shaft or (b) a portion of three armature coils, which are equally arranged, is deleted. However, in the case of item (a), it is difficult to reduce the thickness of the device. Further, there is a possibility that the eccentric disk is disconnected by a vibration and centrifugal force generated at the time of rotation. In the case of item (b), an opposing area between the magnetic flux, which is generated by the magnetic field magnet, and the coil of the armature is substantially decreased. Therefore, a ratio of the input to the output of the motor is deteriorated. From the above reasons, it is required to develop another eccentric mechanism.
On the other hand, concerning the motor to be used, investigations are made into not only a DC brush motor but also other various types of motors.
Life of a brushless motor is long, that is, reliability of a brushless motor is high because the brushless motor has no brushes. It is possible to adjust a vibration of the brushless motor by controlling its rotating speed with frequency. Therefore, the structure can be made simple.
Especially, in the case of a cellular phone, since it is necessary to incorporate various functions into the cellular phone, the number of elements mounted on the integrated circuit and the capacity of the memory are exponentially increased. Therefore, it is easy to incorporate a simple circuit into the cellular phone.
FIGS. 7A to 7C are arrangement views showing a flat type vibration motor in the related art. Concerning this vibration motor, for example, refer to JP-A-2000-262969. FIG. 7A is a plan view of the rotor, FIG. 7B is a sectional view of the rotor and FIG. 7C is a sectional view of the vibration motor.
In a vibration motor 101 shown in FIGS. 7A to 7C, a bearing device 103 is engaged in the central opening of a printed circuit board 102. A stator core 104 is engaged with and fixed to this bearing device 103.
A cover 105 is formed into a substantial cup-shape and its peripheral portion is engaged with the periphery of the printed circuit board 102.
A stator 106 includes a stator core 104 and a coil 107 wound around the stator core 104.
A rotor 110 includes: a magnet 109; a magnetic path yoke 111; and an imbalance weight 108. The imbalance weight 108 is attached inside the cup-shaped rotor 110 above the magnet 109. The magnet 109 is arranged on the outer circumference of the stator core 104 being opposed to each other while leaving a gap between the magnet 109 and the stator core 104. In the magnetic path yoke 111, an inside ring portion 112 and an outside ring portion 115, in which an annular plate portion 113 and an cylindrical portion 114 are continuously provided, are connected with each other by three spoke portions 116. On the inside of the magnetic path yoke 111 on the side to which the cylindrical portion 114 is connected, the arcuate imbalance weight 108 is provided. On the opening side of the cylindrical portion 114, the annular magnet 109, which prevents the imbalance weight 108 from coming out, is provided.
The imbalance weight 108 is arranged in an upper portion in the axial direction of the magnet 109. According to this structure, the imbalance weight 108 is accommodated in an empty space of the circumference opposed type motor having a core. Therefore, the volume of the entire vibration motor can be reduced. Accordingly, it is possible to obtain a small light motor. Further, since the imbalance weight 108 is housed inside the rotor 110, there is no possibility that the imbalance weight is disconnected. Therefore, it is possible to provide a highly reliable motor. Since it is possible to increase diameters of the magnet 109 and the stator core 104, a motor output per unit mass can be increased. In other words, the weight of the vibration motor can be further reduced.
The vibration motor shown in FIGS. 7A to 7C is preferable because the imbalance weight 108 is not disconnected since the imbalance weight 108 is housed inside the rotor 110. However, the following problems may be encountered.
(1) Since the imbalance weight 108 is housed inside the rotor 110, it is necessary to manufacture both the imbalance weight 108 and the rotor 110 at high dimensional accuracy. Therefore, the number of the manufacturing processes is increased.
(2) It is necessary to attach the imbalance weight 108 at an appropriate position so that an unnecessary vibration can not be generated at the time of rotating the rotor and so that the attaching portion can not be damaged and the imbalance weight 108 can not be freely moved, that is, high dimensional accuracy is required for assembling the vibration motor.
(3) Since the imbalance weight 108 is partially located only on the upper side of the shaft 117, vibration is also generated in the axial direction, and it is impossible to effectively pick up vibration in the radial direction, that is, the efficiency is low.
(4) Since the imbalance weight 108 is formed into a body different from the rotor 110, it is necessary to provide a special process in which the imbalance weight 108 is incorporated into the rotor 110.
(5) On the upper face side of the rotor 110, the inside ring portion 112 and the annular plate portion 113 of the outside ring portion 115 are connected to each other by three spoke portions 116. Therefore, opening portions 118 are formed. Due to these opening portions 118, when the imbalance weight 108 is attached to the rotor 110, the attaching area is decreased. As a result, the supporting strength is lowered.
It can be considered that the above problems are originated from the fact that the imbalance weight 108 is formed into a body different from the rotor 110. Therefore, from the viewpoint of integrating the imbalance weight 108 with the rotor 110 into one body, the related art is surveyed as follows. For example, the vibration motor shown in FIGS. 8A to 8C is provided.
FIGS. 8A to 8C are arrangement views of a flat coreless vibration motor in the related art. For example, this vibration motor is shown in JP-A-09-093862. FIG. 8A is a perspective view of the rotor in which an eccentric ring is arranged, FIG. 8B is a perspective view of the eccentric ring and FIG. 8C is a sectional view of the flat coreless vibration motor.
In a flat coreless vibration motor 120 shown in FIGS. 8A to 8C, a ring 122 is arranged on the outer circumference of a rotor 121. A deformed portion 123, the gravity center of which is eccentric, is formed in a portion of the ring 122. A protruding portion, which protrudes to an outer circumferential space 125 of a field magnet 124, is formed.
In this example, only the ring 122 having the deformed portion 123, which forms an eccentric gravity center, is engaged with the outer circumference of the rotor 121. Therefore, it is unnecessary to conduct machining for the eccentric gravity center on the rotor 121 itself Accordingly, this structure is advantageous in that the manufacturing cost is reduced.
However, even in this example in which the deformed portion 123 is formed integrally with the rotor 121, the following problems may be encountered.
(1) Since the deformed portion 123 is formed in the ring 122, the outer circumferential shape of which is the same as that of the rotor 121, it is easy to manufacture the ring 122 and the deformed portion 123. However, an objective portion of the rotor 121, to which the ring 122 is attached, that is, a portion 128, in which three coils 126a, 126b, 126c including a shaft 127 are integrally formed by means of molding of engineering plastics, must be formed into a body different from the ring 122 made of metal. Therefore, the number of processes of forming those components into the rotor 121 is increased.
(2) Since the deformed portion 123 is formed in the ring 122, the outer circumferential shape of which is suited to that of the rotor 121, it is easy to manufacture the ring 122 and the deformed portion 123. However, an objective portion of the rotor 121, to which the ring 122 is attached, that is, a portion 128, in which three coils 126a, 126b, 126c including the shaft 127 are integrally formed by means of molding of engineering plastics, has an expansion coefficient different from that of the ring 122 made of metal. Accordingly, there is a possibility that a portion 128 concerned and the ring 122 are separated from each other and vibration is generated. Since the different materials are used, there is a possibility of the poor mechanical strength.
(3) The outer circumferential space 125 must be formed on the outer circumferential side of the magnetic field magnet 124. Therefore, the shape of the magnetic field magnet 124 is restricted and the obtained magnetic force is restricted.
(4) Since the rotor 121 is of the axial direction opposed type in this example, the coils 126a, 126, 126c are arranged in the rotor 121. Therefore, when the ring 122 is provided in the rotor 121, the coils 126a, 126b, 126c as well as the ring 122 must be provided in the rotor 121. As a result, since the coils 126a, 126b, 126c are provided in the rotor 121, it is impossible to form the rotor 121 out of the same material as that of the ring 122.
(5) In this example, the vibration motor is provided with a brush 129 and a commutator 130, the brush 129 may be damaged and contaminated. Further, at the time of starting and stopping, the rotating speed is changed and it is impossible to maintain the rotating speed constant.
Although the above problems are encountered, DC motor having a brush has been used for generating vibration of a cellular phone until now.
The reason why is described as follows. Since the semiconductor integration technique was in retard, it was difficult to specially manufacture a circuit containing a motor control circuit in a small cellular phone. Therefore, DC motor having no brushes, the price of which is low, in which trouble seldom occurs, has been mainly used.
Concerning the coin type, the thickness can be reduced, however, the life is short and it is difficult to control it because the starting and the stopping time are long.
In order to solve the above problems, it can be considered to use a stepping motor, the control circuit structure of which is simple and the rotating speed control of which is easy at the time of starting and stopping, as a vibration motor. However, the stepping motor is used as a vibration motor only for a special use.
FIGS. 9A to 9C are arrangement view showing a vibration motor in which a stepping motor in the related art is used. Concerning this vibration motor, for example, refer to JP-A-2004-320941. FIG. 9A is a plan view showing a main portion, wherein this view is taken when the resin base side is seen from the permanent magnet side. FIG. 9B is a perspective view of the rotor yoke. FIG. 9C is a sectional view.
A stepping motor 140 shown in FIGS. 9A to 9C includes: a stator 145 in which a flat coreless coil 144 is provided on a resin base 141 via a stator yoke 142 and a circuit board 143; and a rotor 150 having a permanent magnet 149, which is arranged on a rotor yoke 148 having a rotary shaft 147 pivotally supported by the stator 145 via a bearing 146, wherein this permanent magnet 149 is arranged while leaving a predetermined gap with respect to the coreless coil 144 in the axial gap system.
The ring-shaped stator yoke 142 made of magnetic material and the flexible ring-shaped circuit board 143, which is a wiring portion, are fixed to the disk-shaped resin base 141 made of resin material by means of molding. This circuit board 143 is made of insulating material, and the four flat coreless coils 144, the shapes of which are respectively formed into a sector-shape when they are seen in a plan view, are arranged on the circuit board 143 round the rotary center L of the rotor 150 described later at regular intervals of 90°.
The rotor yoke 148, which is a magnetic thin sheet, is made of magnetic material and formed into a disk-shape by means of molding. On this rotor yoke 148, the annular permanent magnet 149 is mechanically fixed. Six poles of the permanent magnet 149 are arranged around the rotation center L at regular intervals of 60° so that N-pole and S-pole can be alternately located to be different magnetic poles from each other.
When a weight member 151 is fixed at a position of the rotor yoke 148 which is eccentric with respect to the rotation center L of the rotor 150 and this rotor 150 is rotated, the vibration motor can be applied to a cellular phone or a toy.
The following problems may be encountered in the vibration motor using the above stepping motor.
(1) The rotor yoke 148 of the rotor 150 and the weight member 151 must be respectively formed into different bodies and combined with each other. Therefore, high dimensional accuracy is required for the rotor yoke 148 and the weight member 151. Further, it is necessary to provide an assembling process of assembling the bodies which are formed differently from each other.
(2) It is necessary to precisely detect the eccentric position of the rotor yoke 148. It is also necessary to strongly fix the weight member 151 at the eccentric position. Therefore, the positioning work is required and further the manufacturing process is increased.
(3) Since the coreless coil 144 is used, the coil size can not be reduced and the number of the magnetic poles can not be increased. Accordingly, the number of steps can not be increased. Since the coreless structure is adopted, permeance of the magnetic circuit is low and a quantity of the permanent magnet to be used is increased.
(4) Since the magnetic circuit composed of the permanent magnet 149 and the coreless coil 144 is of the axial direction opposed type, an intensity of the magnetic force for rotation is lower than that of the radial direction opposed type. Therefore, it is difficult to pick up the vibration strongly and effectively. Since the weight member 151 is arranged outside the rotor yoke 148 and the size of the weight member 151 is small, it is impossible to pick up the vibration strongly and effectively.